The present invention relates to blind fasteners and, more particularly, to blind fasteners employed to join composite materials.
Blind fasteners of the general type shown herein are well known in the art. As used in joining materials such as aluminum used in more conventional aircraft, blind side damage had to be considered but was not of major concern.
More recently, constructions of aircraft and the like employing panels of composite materials such as graphite and fiber/epoxy matrix are more common. The problem of blind side damage and fasteners to provide strong mechanical joining with a minimum of blind side damage has become an area of focus within the art. U.S. Pat. No. 4,203,346 to Hall, et al, and U.S. Pat. No. 4,033,222 to Wilson (also assigned to the common assignee of this application) both address blind fasteners directed toward this problem area. FIGS. 1 and 2 herein are directed towards the subject matter of the Hall, et al. patent while FIGS. 3 and 4 are directed to the most relative teaching from the Wilson patent.
Turning first to FIGS. 1 and 2, it can be seen that the blind fastener, generally indicated as 10, of the Hall teaching comprises three portions. A nut, generally indicated as 12, a sleeve, generally indicated as 14, and a corebolt, generally indicated as 16. The nut comprises a head 18, a first cylindrical portion 20 adjacent the head 18, a second cylindrical portion 22 adjacent first portion 20 and a beveled nose portion 24 on the end opposite head 18. Sleeve 14 comprises a first portion 26 having a constant thickness wall about an internal bore 28 of slightly larger diameter than the threaded portion of corebolt 16 and a second portion 30 having an interal bore 32 tapering outward such that the walls become increasingly thinner. Corebolt 16 has a threaded portion 34 and a head 36. With sleeve 14 slid onto corebolt 16 and bolt 16 threaded into nut 12, the fastener 10 is passed through a plurality of panels, generally indicated as 38, as shown in FIG. 2. As the nut 12 and corebolt 16 are threaded together, the sleeve 14 is firmly abutted against head 36 on one end and against a specially provided shoulder 40 where first cyclindrical portion 20 and second cyclindrical portion 22 of nut 12 meet on the other end. As nut 12 and corebolt 16 are thereafter further threadedly engaged, sleeve 14 is put under a compressive force causing second portion 30 thereof to buckle radially outward in the manner shown in FIG. 2. This action, provided by the shoulder 40 on the nut 12 eliminates the so-called "cookie-cutter" effect which occurs when a sleeve is forced against the composite material of the innermost panel 38 for its compressive force.
Turning next to the prior art fastener of FIGS. 3 and 4, once again, the fastener generally indicated as 42, has a nut portion, generally indicated as 44, and a corebolt portion, generally indicated as 46. The nut 44 has a head 48, a body portion 50 and a nose portion 52. The body portion 50 is of a diameter so as to be a clearance fit when passed through a common bore 54 located in a plurality of panels 56. The bolt 46 has a head 58 and a threaded portion 60. A pair of sleeves 62 are disposed on the threaded portion 60. The first sleeve, generally indicated as 64, is disposed adjacent nut 44 and comprises a cyclindrical body portion 66 and a tapered nose portion 68. Tapered nose portion 68 faces in the same direction as the nose portion 52 of nut 44. The second sleeve 70 also has a cylindrical body portion 72. First sleeve 64 is made of a more ductile material than second sleeve 70 whereby as nut 44 is disposed within bore 54 and threadily engaged with corebolt 46 to compress sleeves 64, 70 between the heads 48,58, first sleeve 64 will more readily deform and, therefore, will be deformed along the blind side of panels 56 to form a protective surface 76 against which second sleeve 70 is deformed as nut 44 and bolt 46 are continued in their threaded engagement whereby the assembled state as shown in FIG. 4 is finally created.
The prior art fastener of FIGS. 1 and 2 requires that the nut 12 and sleeve 14 thereof be specially constructed. The fastner of FIGS. 3 and 4 produces some unprotected bearing of the first sleeve 64 against the blind side of the panels 56 adjacent bore 54.
Wherefore, it is the object of the present invention to provide a blind fastener for use with composite material panels which is simple in nature, inexpensive to manufacture, provides no direct bearing against the blind side, and is of a design such as to allow the use of existing tooling in the inventory of users to a maximum.